1. Autosomal dominant inheritance All affected individuals should have an affected parent Both sexes should be equally affected Roughly 50% of the offspring of an affected individual should also be affected Huntington’s disease, Achondroplastic dysplasia, Neurofibromatosis.

2. A large autosomal dominant pedigree!

3. Autosomal Recessive Inheritance Usually there is no previous family history The most likely place to find a second affected child is a sibling of the first

4. Autosomal recessive Inbreeding increases the chance of observing an autosomal recessive condition E.g. Cystic fibrosis, sickle cell disease, Tay Sachs disease.

5. Exceptions to clear cut Mendelian inheritance Lethal alleles T/+ x T/+ T/T T/+ +/+1 : 2 : 1 ratio at conception 0 : 2 : 1 ratio at birth

6. Exceptions to clear cut Mendelian inheritance Lethal alleles Incomplete dominance Familial Hypercholesterolemia +/+ = normal +/- = death as young adult -/- = death in childhood

7. Exceptions to clear cut Mendelian inheritance Lethal alleles Incomplete dominance Codominance Silent alleles

8. Exceptions to clear cut Mendelian inheritance Lethal alleles Incomplete dominance Codominance Silent alleles Epistasis The Bombay Phenotype: The ABO blood group genotype cannot be deduced in h/h homozygotes.

9. Exceptions to clear cut Mendelian inheritance Lethal alleles Incomplete dominance Codominance Silent alleles Epistasis Pleiotropy genetic heterogeneity

10. Exceptions to clear cut Mendelian inheritance Lethal alleles Incomplete dominance Codominance Silent alleles Epistasis Pleiotropy genetic heterogeneity variable expressivity incomplete penetrance

11. Exceptions to clear cut Mendelian inheritance Lethal alleles Incomplete dominance Codominance Silent alleles Epistasis Pleiotropy genetic heterogeneity variable expressivity incomplete penetrance Anticipation E.g. Myotonic dystrophy

12. Exceptions to clear cut Mendelian inheritance Lethal alleles Incomplete dominance Codominance Silent alleles Epistasis Pleiotropy genetic heterogeneity variable expressivity incomplete penetrance Anticipation germline mosaicism phenocopies Phocomelia Incomplete ascertainment mitochondrial inheritance

13. Mitochondrial inheritance

14. Exceptions to clear cut Mendelian inheritance Lethal alleles Incomplete dominance Codominance Silent alleles Epistasis Pleiotropy Genetic heterogeneity Variable expressivity Incomplete penetrance Anticipation Reverse anticipation Germline mosaicism Phenocopies Mitochondrial inheritance Uniparental disomy Linkage